1. Field of the Invention
The present invention relates to a contactor failure detecting apparatus for a fuel cell, for detecting failure of a contactor provided between the fuel cell and a load that is supplied with electrical energy from the fuel cell, wherein the contactor serves for connecting or disconnecting the load with the fuel cell.
2. Description of the Related Art
For example, a polymer electrolyte fuel cell employs a membrane electrode assembly, which includes an anode (fuel electrode) and a cathode (air electrode), and a polymer electrolyte membrane interposed between the electrodes. The electrolyte membrane acts as an ion exchange membrane. The membrane electrode assembly is sandwiched between a pair of separators. A fuel gas flow field is formed between the anode and one of the separators, and an oxygen-containing gas flow field is formed between the cathode and the other separator. In use, normally, a predetermined number of membrane electrode assemblies and separators are stacked together to form a fuel cell stack.
In the fuel cell, a fuel gas such as a hydrogen-containing gas is supplied to the fuel gas flow field. The fuel gas flows through the fuel gas flow field along the anode. The catalyst of the anode induces a chemical reaction of the fuel gas, so as to split hydrogen molecules into hydrogen ions and electrons. The hydrogen ions move toward the cathode through a suitably humidified electrolyte membrane, and the electrons flow through an external circuit to the cathode, thereby creating DC electrical energy. An oxygen-containing gas such as air is supplied to the oxygen-containing gas flow field, wherein the oxygen-containing gas flows along the cathode for inducing a reaction. At the cathode, hydrogen ions from the anode combine with electrons and oxygen to produce water. Water is retained at the anode as a result of back diffusion from the cathode, high humidification of the fuel gas, or the like.
If water is retained excessively at either of the electrodes, water clogging may occur, thereby reducing the power generation efficiency of the fuel cell system. Heretofore, there has been proposed a technique for scavenging both sides of the anode and cathode, as disclosed in Japanese Laid-Open Patent Publication No. 2003-331893. In the above technique, operation of the fuel cell system is started or stopped in order to achieve a desired performance when initiating a subsequent operation of the fuel cell system, wherein oxygen-containing gas is supplied to the anode as well as to the cathode, for removing water produced during power generation from the membrane electrode assembly or from the fuel cell separators.
Also, as disclosed in Japanese Laid-Open Patent Publication No. 2-51868, a fuel cell system includes a contactor that acts as an opening and closing switch, disposed between the fuel cell and a load supplied with electrical energy from the fuel cell. Such a fuel cell system further includes an auxiliary power supply for supplying electrical energy to auxiliary device loads, such as a CPU, an air compressor, a pump, a valve, a heater, etc., when operation of the fuel cell is started and stopped.
When the fuel cell system is applied to a vehicle, according to one proposal, an energy storage device serving as an auxiliary power supply is mounted in the vehicle in parallel with the fuel cell for driving the motor. This technique is adopted, e.g., for achieving a desired response in the fuel cell system, when the fuel cell system is operated variably in accordance with an input for the driving power, and for supplying electrical energy to auxiliary device loads, such as an air compressor of the fuel cell system, when operation of the fuel cell is started, wherein the energy storage device is charged using regenerative energy of the motor when the vehicle is decelerated, so as to use the energy for assistance during a subsequent acceleration, thereby achieving an improvement in fuel cell vehicle efficiency.
Further, the fuel cell system includes a contactor disposed between the fuel cell and a load supplied with electrical energy from the fuel cell, for connecting or disconnecting the load from the fuel cell. In this case, when a relatively large load is connected to the fuel cell, a movable contact of the contactor often becomes meltingly adhered to a fixed contact thereof. Stated otherwise, there is the disadvantage that a “closing failure” may occur.
However, a technique for detecting closing failure due to such melting adhesion, etc., of the contactor provided between the fuel cell and the load has heretofore been unknown.